This invention relates to an apparatus for simulating the effect of gravity on light and to a method for constructing said apparatus. More particularly, the apparatus comprises a lens for simulating the effect when light from a distant source passes through a gravity field such as that from a spherical galaxy having a certain structure. Furthermore, the invention also relates to a description of the shape necessary to mimick the effect, and to the method of using such a lens to simulate the desired effect.
The bending effect of gravity on light rays was originally predicted by Albert Einstein, from which it follows that a gravity field would mimic a lens and produce images. More specifically, the effect of gravity on light from a source not only would make the light source appear out of position, but it could also produce multiple images of a single source. Thus, to a properly positioned observer, a distant quasar would appear as triplets or quintuplets if its light passed through a galaxy of a certain structure.
The theory behind the bending of light as a result of gravity has led to attempts to construct a lens capable of mimicking the distortion caused by such a field. One such lens is disclosed in, Construction of a Gravitational Lens; Am. J. Phys., Vol. 48, NO. 10, October 1980 pg. 883. In this article, a cylindrical gravitational lens is described for imitating the effect of the gravity field from a black hole. The lens is rotationally symmetric, flat on one side, and on the other side has a surface that obeys the equation: EQU T=[2R/(n-1)] log (r.sub.o /r),
wherein T is the thickness of the lens, R corresponds to the Schwarzschild radius of the black hole being imitated, n is the index of refraction of the lens material, r.sub.o is the maximum possible radius of the lens, and r is the distance between the lens axis and the point at which the thickness T is measured. FIG. 1 schematically shows the cross-section of such a lens. This lens will be referred to hereinafter as a "cusp" shaped lens. Although the lens described in the above-discussed article is described as fairly accurately mimicking the effect of a black hole on light passing through its gravity field, it is ineffective to mimick the more common effect of the gravitational field of a galaxy on light passing therethrough.
Another structurally related prior art device is known as a Schmidt corrector plate developed by B. Schmidt around 1930, and discussed in the textbook Principles of Optics, by Born and Wolf, Pergamon Press. More particularly, the Schmidt corrector plate is employed in photographing wide angular fields and has a form somewhat similar to that of the above-discussed gravitational lens. However, even though the general shape of a Schmidt corrector plate is similar to that of a gravitational lens, it is not useful as a lens for simulating the discussed gravity effect on light because its focal length (typically 0.7 kilometers) is much greater than the distance between the observer and the gravitational lens (typically 15 cm to 75 cm), and therefore in the case of the Schmidt corrector plate, it is impossible to observe the multiple imaging effect over a useful distance range.